DS00795A-page 13

© 2002 Microchip Technology, Inc.

AN795

FIGURE 26: Circuit uses frequency-to-voltage-to-frequency conversion, with intermediate stage of gain between conversions, for

multiplying input frequency by any number. Digital-to-analog converter is programmed digitally, by thumbwheel switches or microcontroller,

for coarse selection of frequency-multiplying factor; op-amp provides fine gain, enables choice of non-integer multiplication values.

*Reprinted with permission from Electronics, October 12, 1978; Copyright © Mc-Graw-Hill, Inc., 1978. All rights reserved.

TC9400

Frequency-

to-Voltage

Converter

Comp In

Offset

Gnd

Amp

Out

DAC-03

Digital-to-Analog

Converter

Offset

Gnd

Out

Amp Out

Comp In

Gnd

Analog

Gnd

MSB

LSB

+

–

1

2

3

4

5

6

7

8

9

10

+5V

Digital

Gain Factor

(Programmable)

–5V

100k

Ω

10k

Ω

10

14

6

1

7

4

50k

Ω

14

6

3

2

–15V

+15V

12

11

3

5

180pF

180pF

9

2

6

2

14

+5V

+5V

1

7

4

11

20k

Ω

5

3

12

47pF

0.1

µF

1M

Ω

15

1M

Ω

100k

Ω

TC9400

Frequency-

to-Voltage

Converter

17

18

16

12

11

13

+15V

–15V

MSB = Most Significant Bit

LSB = Least Significant Bit

100k

Ω

2.2k

Ω

10k

Ω

510k

Ω

Op

Amp